1. Field of the Invention
The present invention relates to a process for preparing a modified resin useful as a low-stress semiconductor encapsulant for improving the reliability of material used in semiconductor encapsulation by utilizing a molding process and the like, as well as to a modified resin composition produced therefrom.
2. Description of the Prior Art
Molding compounds useful for semiconductor encapsulation of large-scale semiconductor devices, large size chips, and small size memory cells have been developed for improving moisture resistance, lowering stress, and reducing radiation of alpha particles thereof. However, such molding compounds suffer from a number of problems. For example, it is very difficult for a semiconductor encapsulant made of a thermosetting resin, such as an epoxy resin, to exhibit a minimized volume-change during the molding process, a minimized linear thermal-expansion coefficient when compared with the coefficient of enclosed metal parts, or a desired compatibility with the other components. Further, the resin usually lacks desired thermal resistance, moisture resistance, and crack resistance, and insufficiently protects semiconductor parts and the wire bonds therewithin from internal shock and the external environment.
Generally, an epoxy resin is used as a thermosetting resin since it has many desired electrical and mechanical properties, and exhibits chemical resistance. However, it exhibits undesired flexibility after curing so that an elastic rubber or the like is added to the epoxy resin by blending or reacting the rubber with the epoxy resin to overcome this problem.
In spite of this, the resulting blend exhibits many defects such as, for example, a larger thermal-expansion rate and a reduced flowing property when the rubber is added alone to the epoxy resin. Also a tacky or stained curing surface results due to the curability difference, as well as reduced molding time.
In another method, a silicone oil or silicone resin intermediate is simply added to the epoxy resin or a phenol resin for reducing the linear-expansion coefficient when compared with the inorganic material. However, many problems arise such as, for example, non-uniform dispersion conditions due to an incompatibility with the other composition parts, a reduction in strength of the cured product, and a reduction in bondability with the metal parts, whereby the reliability of the resulting semiconductor device is greatly reduced.
A method for producing an addition product of a coupling agent and an inorganic filler is already known. This method is used to improve moisture resistance and to reinforce strength. However, it is unsatisfactory with respect to absorbing and reducing the stress caused by increased modulus, and also, if an excess amount of coupling agent is used, a stain appears since the absorbtion capability is limited and some of the remaining coupling agent reacts with organic binders which causes voids to be formed during the molding process.